Changed the fluid in my 11.5 rear end and used Mobil 1 Full syn. 75w-90. I have since read that the AAM rear end may call for something different. Manual calls for GL-5 syn. I believe. Mopar's fluid says for use in AAM axels. Is this marketing hype or legidement need?

75w90 will be just fine unless you are pulling heavy in hot ambient temps a lot.

75w90 will be just fine unless you are pulling heavy in hot ambient temps a lot.

I'm in the South and will pull 14K about once a month 50 miles or less at 55-60mph or less on secondary roads.

Wild and Free is correct. I use Amsoil 75W 90 gear lube in both my diffs. 163,000 on the clock now and no problems!!

I have called and talked to AAM and they spec 75w-90 for all loads/temps. They said if you live well above GCWR and tow thru death valley most the time then 75w-140 would be better, otherwise stick to 75w-90. Even the max tow (GCWR of 30K) uses 75w-90, but with a finned cover.